1. Field of the Invention
The present invention relates to a refrigeration or air conditioning system that uses a refrigerant alternative to R22.
2. Related Art
It is becoming more desirable that the working mediums in recently developed refrigeration equipment consisting of a compressor, a condenser, a throttling device, an evaporator, an accumulator, etc. be changed from the traditional chloroflurocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants, which are said to have harmful effects on the ozone layer, to hydrofluorocarbon (HFC) refrigerants which are alternative refrigerants claimed to pose no threats to the ozone layer.
Especially, the working medium in air conditioning, refrigerant mixtures consisting of an HFC refrigerant R32 (difluoromethane, CH.sub.2 F.sub.2 boiling point -51.66.degree. C.) and an HFC refrigerant R125 (pentafluoroethane, CF.sub.3 -CHF.sub.2, boiling point -48.14.degree. C.) have been drawing attention as potential substitutes for R22, an HCFC refrigerant. A refrigerant mixture consisting of 50.+-.-2 weight percent of R32 and 50.+-.-2 weight percent of R125 is called R410A and is treated as if it were a single refrigerant.
Historically, when a refrigeration cycle system containing R410A was operated, there occurred the problem that the refrigerant reacted with a small amount of water in the refrigeration cycle system, forming a clathrate (sometimes called an enclosure compound or hydrate) which froze the line from the evaporator outlet through to the compressor suction line. In particular, if the small oil return port provided on the accumulator is frozen, the oil will not circulate into the compressor, and reliability will be seriously affected.
The clathrate here is defined as "a substance in which atoms or molecules are trapped in appropriately sized holes in a three-dimensional structure formed from other atoms or molecules bonded together, thus forming a particular crystal structure." Host solution is a substance that forms the skeleton of the three-dimensional structure, and usually water acts as the host solution. Guest molecules fill the inside of the skeleton and stabilize the ice structure of the clathrate, making its formation possible at temperatures much higher than the freezing point of water (0.degree. C.). The clathrate structure usually depends on the size of the guest molecules, but its formation condition (temperature and pressure) and extinction condition (critical decomposition point) differ among individual guest molecules.
WO patent specification No. 93/04139 discloses that R32 and R125 create clathrates, but does not clarify the formation conditions of the clathrates created from R32 and R125 as single refrigerants or as a refrigerant mixture.
For the clathrates formed from water and R32, reference can be made to Table 1 on page 123 in Felix Franks, "Water--A Comprehensive Treatise," Plenum Press (1973) which discloses that the critical decomposition temperature is 17.6.degree. C., but no mention is made there of the critical decomposition pressure or the formation condition (temperature and pressure).
On the other hand, regarding the clathrates formed from water and R125, no examples relating to the their formation have been found, let alone examples disclosing the formation and extinction conditions for R32/R125 refrigerant mixture.